fts fts_open fts_read fts_children fts_set fts_close - traverse a file hierarchy

from : http://linux.about.com/library/cmd/blcmdl3_fts_open.htm

Fd #include <sys/types.h> Fd #include <sys/stat.h> Fd #include <fts.h> Ft FTS * Fn fts_open char * const *path_argv int options int (*compar)(const FTSENT **, const FTSENT **) Ft FTSENT * Fn fts_read FTS *ftsp Ft FTSENT * Fn fts_children FTS *ftsp int options Ft int Fn fts_set FTS *ftsp FTSENT *f int options Ft int Fn fts_close FTS *ftsp  

DESCRIPTION

The  fts  functions are provided for traversing  UNIX  file hierarchies. A simple overview is that the Fn fts_open function returns a ``handle'' on a file hierarchy, which is then supplied to the other fts  functions. The function Fn fts_read returns a pointer to a structure describing one of the files in the file hierarchy. The function Fn fts_children returns a pointer to a linked list of structures, each of which describes one of the files contained in a directory in the hierarchy. In general, directories are visited two distinguishable times; in pre-order (before any of their descendants are visited) and in post-order (after all of their descendants have been visited). Files are visited once. It is possible to walk the hierarchy ``logically'' (ignoring symbolic links) or physically (visiting symbolic links), order the walk of the hierarchy or prune and/or re-visit portions of the hierarchy.

Two structures are defined (and typedef'd) in the include file Aq Pa fts.h . The first is Fa FTS , the structure that represents the file hierarchy itself. The second is Fa FTSENT , the structure that represents a file in the file hierarchy. Normally, an Fa FTSENT structure is returned for every file in the file hierarchy. In this manual page, ``file'' and ``Fa FTSENT structure '' are generally interchangeable. The Fa FTSENT structure contains at least the following fields, which are described in greater detail below:

typedef struct _ftsent {
        u_short fts_info;               /* flags for FTSENT structure */
        char *fts_accpath;              /* access path */
        char *fts_path;                 /* root path */
        short fts_pathlen;              /* strlen(fts_path) */
        char *fts_name;                 /* file name */
        short fts_namelen;              /* strlen(fts_name) */
        short fts_level;                /* depth (-1 to N) */
        int fts_errno;                  /* file errno */
        long fts_number;                /* local numeric value */
        void *fts_pointer;              /* local address value */
        struct ftsent *fts_parent;      /* parent directory */
        struct ftsent *fts_link;        /* next file structure */
        struct ftsent *fts_cycle;       /* cycle structure */
        struct stat *fts_statp;         /* stat(2) information */
} FTSENT;

These fields are defined as follows:

Fa fts_info

One of the following flags describing the returned Fa FTSENT structure and the file it represents. With the exception of directories without errors ( FTS_D ) all of these entries are terminal, that is, they will not be revisited, nor will any of their descendants be visited.

FTS_D

A directory being visited in pre-order.

FTS_DC

A directory that causes a cycle in the tree. (The Fa fts_cycle field of the Fa FTSENT structure will be filled in as well.)

FTS_DEFAULT

Any Fa FTSENT structure that represents a file type not explicitly described by one of the other Fa fts_info values.

FTS_DNR

A directory which cannot be read. This is an error return, and the Fa fts_errno field will be set to indicate what caused the error.

FTS_DOT

A file named `.' or `..' which was not specified as a file name to Fn fts_open (see FTS_SEEDOT )

FTS_DP

A directory being visited in post-order. The contents of the Fa FTSENT structure will be unchanged from when it was returned in pre-order, i.e. with the Fa fts_info field set to  FTS_D

FTS_ERR

This is an error return, and the Fa fts_errno field will be set to indicate what caused the error.

FTS_F

A regular file.

FTS_NS

A file for which no  stat(2) information was available. The contents of the Fa fts_statp field are undefined. This is an error return, and the Fa fts_errno field will be set to indicate what caused the error.

FTS_NSOK

A file for which no  stat(2) information was requested. The contents of the Fa fts_statp field are undefined.

FTS_SL

A symbolic link.

FTS_SLNONE

A symbolic link with a non-existent target. The contents of the Fa fts_statp field reference the file characteristic information for the symbolic link itself.

Fa fts_accpath

A path for accessing the file from the current directory.

Fa fts_path

The path for the file relative to the root of the traversal. This path contains the path specified to Fn fts_open as a prefix.

Fa fts_pathlen

The length of the string referenced by Fa fts_path .

Fa fts_name

The name of the file.

Fa fts_namelen

The length of the string referenced by Fa fts_name .

Fa fts_level

The depth of the traversal, numbered from -1 to N, where this file was found. The Fa FTSENT structure representing the parent of the starting point (or root) of the traversal is numbered -1, and the Fa FTSENT structure for the root itself is numbered 0.

Fa fts_errno

Upon return of a Fa FTSENT structure from the Fn fts_children or Fn fts_read functions, with its Fa fts_info field set to  FTS_DNR FTS_ERR or  FTS_NS the Fa fts_errno field contains the value of the external variable  errno specifying the cause of the error. Otherwise, the contents of the Fa fts_errno field are undefined.

Fa fts_number

This field is provided for the use of the application program and is not modified by the  ftsfunctions. It is initialized to 0.

Fa fts_pointer

This field is provided for the use of the application program and is not modified by the  ftsfunctions. It is initialized to  NULL

Fa fts_parent

A pointer to the Fa FTSENT structure referencing the file in the hierarchy immediately above the current file, i.e. the directory of which this file is a member. A parent structure for the initial entry point is provided as well, however, only the Fa fts_level , Fa fts_number and Fa fts_pointer fields are guaranteed to be initialized.

Fa fts_link

Upon return from the Fn fts_children function, the Fa fts_link field points to the next structure in the NULL-terminated linked list of directory members. Otherwise, the contents of the Fa fts_link field are undefined.

Fa fts_cycle

If a directory causes a cycle in the hierarchy (see  FTS_DC ) either because of a hard link between two directories, or a symbolic link pointing to a directory, the Fa fts_cycle field of the structure will point to the Fa FTSENT structure in the hierarchy that references the same file as the current Fa FTSENT structure. Otherwise, the contents of the Fa fts_cycle field are undefined.

Fa fts_statp

A pointer to  stat(2) information for the file.

A single buffer is used for all of the paths of all of the files in the file hierarchy. Therefore, the Fa fts_path and Fa fts_accpath fields are guaranteed to be NULL -terminated only for the file most recently returned by Fn fts_read . To use these fields to reference any files represented by other Fa FTSENT structures will require that the path buffer be modified using the information contained in that Fa FTSENT structure's Fa fts_pathlen field. Any such modifications should be undone before further calls to Fn fts_read are attempted. The Fa fts_name field is always NULL -terminated.  

FTS_OPEN

The Fn fts_open function takes a pointer to an array of character pointers naming one or more paths which make up a logical file hierarchy to be traversed. The array must be terminated by a NULL  pointer.

There are a number of options, at least one of which (either FTS_LOGICAL or FTS_PHYSICALmust be specified. The options are selected by or 'ing the following values:

FTS_COMFOLLOW

This option causes any symbolic link specified as a root path to be followed immediately whether or not  FTS_LOGICAL is also specified.

FTS_LOGICAL

This option causes the  fts routines to return Fa FTSENT structures for the targets of symbolic links instead of the symbolic links themselves. If this option is set, the only symbolic links for which Fa FTSENT structures are returned to the application are those referencing non-existent files. Either  FTS_LOGICAL or  FTS_PHYSICAL  must be provided to the Fn fts_open function.

FTS_NOCHDIR

As a performance optimization, the  fts functions change directories as they walk the file hierarchy. This has the side-effect that an application cannot rely on being in any particular directory during the traversal. The  FTS_NOCHDIR option turns off this optimization, and the  fts functions will not change the current directory. Note that applications should not themselves change their current directory and try to access files unless  FTS_NOCHDIR is specified and absolute pathnames were provided as arguments to Fn fts_open .

FTS_NOSTAT

By default, returned Fa FTSENT structures reference file characteristic information (the Fa statp field) for each file visited. This option relaxes that requirement as a performance optimization, allowing the  fts functions to set the Fa fts_info field to  FTS_NSOK and leave the contents of the Fa statp field undefined.

FTS_PHYSICAL

This option causes the  fts routines to return Fa FTSENT structures for symbolic links themselves instead of the target files they point to. If this option is set, Fa FTSENT structures for all symbolic links in the hierarchy are returned to the application. Either FTS_LOGICAL or  FTS_PHYSICAL  must be provided to the Fn fts_open function.

FTS_SEEDOT

By default, unless they are specified as path arguments to Fn fts_open , any files named `.' or `..' encountered in the file hierarchy are ignored. This option causes the  fts routines to return Fa FTSENT structures for them.

FTS_XDEV

This option prevents  fts from descending into directories that have a different device number than the file from which the descent began.

The argument Fn compar specifies a user-defined function which may be used to order the traversal of the hierarchy. It takes two pointers to pointers to Fa FTSENT structures as arguments and should return a negative value, zero, or a positive value to indicate if the file referenced by its first argument comes before, in any order with respect to, or after, the file referenced by its second argument. The Fa fts_accpath , Fa fts_path and Fa fts_pathlen fields of the Fa FTSENT structures may never be used in this comparison. If the Fa fts_info field is set toFTS_NS or FTS_NSOK the Fa fts_statp field may not either. If the Fn compar argument is NULLthe directory traversal order is in the order listed in Fa path_argv for the root paths, and in the order listed in the directory for everything else.  

FTS_READ

The Fn fts_read function returns a pointer to an Fa FTSENT structure describing a file in the hierarchy. Directories (that are readable and do not cause cycles) are visited at least twice, once in pre-order and once in post-order. All other files are visited at least once. (Hard links between directories that do not cause cycles or symbolic links to symbolic links may cause files to be visited more than once, or directories more than twice.)

If all the members of the hierarchy have been returned, Fn fts_read returns NULL and sets the external variable errno to 0. If an error unrelated to a file in the hierarchy occurs, Fn fts_read returns NULL and sets errno appropriately. If an error related to a returned file occurs, a pointer to an Fa FTSENT structure is returned, and errno may or may not have been set (see Fa fts_info ) .

The Fa FTSENT structures returned by Fn fts_read may be overwritten after a call to Fn fts_close on the same file hierarchy stream, or, after a call to Fn fts_read on the same file hierarchy stream unless they represent a file of type directory, in which case they will not be overwritten until after a call to Fn fts_read after the Fa FTSENT structure has been returned by the function Fn fts_read in post-order.  

FTS_CHILDREN

The Fn fts_children function returns a pointer to an Fa FTSENT structure describing the first entry in a NULL-terminated linked list of the files in the directory represented by the Fa FTSENT structure most recently returned by Fn fts_read . The list is linked through the Fa fts_link field of the Fa FTSENT structure, and is ordered by the user-specified comparison function, if any. Repeated calls to Fn fts_children will recreate this linked list.

As a special case, if Fn fts_read has not yet been called for a hierarchy, Fn fts_children will return a pointer to the files in the logical directory specified to Fn fts_open , i.e. the arguments specified to Fn fts_open . Otherwise, if the Fa FTSENT structure most recently returned by Fn fts_read is not a directory being visited in pre-order, or the directory does not contain any files, Fn fts_children returns NULL and sets errno to zero. If an error occurs, Fn fts_children returnsNULL and sets errno appropriately.

The Fa FTSENT structures returned by Fn fts_children may be overwritten after a call to Fn fts_children , Fn fts_close or Fn fts_read on the same file hierarchy stream.

Option may be set to the following value:

FTS_NAMEONLY

Only the names of the files are needed. The contents of all the fields in the returned linked list of structures are undefined with the exception of the Fa fts_name and Fa fts_namelen fields.

 

FTS_SET

The function Fn fts_set allows the user application to determine further processing for the file Fa f of the stream Fa ftsp . The Fn fts_set function returns 0 on success, and -1 if an error occurs. Option  must be set to one of the following values:

FTS_AGAIN

Re-visit the file; any file type may be re-visited. The next call to Fn fts_read will return the referenced file. The Fa fts_stat and Fa fts_info fields of the structure will be reinitialized at that time, but no other fields will have been changed. This option is meaningful only for the most recently returned file from Fn fts_read . Normal use is for post-order directory visits, where it causes the directory to be re-visited (in both pre and post-order) as well as all of its descendants.

FTS_FOLLOW

The referenced file must be a symbolic link. If the referenced file is the one most recently returned by Fn fts_read , the next call to Fn fts_read returns the file with the Fa fts_info and Fa fts_statp fields reinitialized to reflect the target of the symbolic link instead of the symbolic link itself. If the file is one of those most recently returned by Fn fts_children , the Fa fts_info and Fa fts_statp fields of the structure, when returned by Fn fts_read , will reflect the target of the symbolic link instead of the symbolic link itself. In either case, if the target of the symbolic link does not exist the fields of the returned structure will be unchanged and the Fa fts_info field will be set to  FTS_SLNONE

If the target of the link is a directory, the pre-order return, followed by the return of all of its descendants, followed by a post-order return, is done.

FTS_SKIP

No descendants of this file are visited. The file may be one of those most recently returned by either Fn fts_children or Fn fts_read .

 

FTS_CLOSE

The Fn fts_close function closes a file hierarchy stream Fa ftsp and restores the current directory to the directory from which Fn fts_open was called to open Fa ftsp . The Fn fts_close function returns 0 on success, and -1 if an error occurs.   

ERRORS

The function Fn fts_open may fail and set  errno  for any of the errors specified for the library functions  open (2) and  malloc (3).

The function Fn fts_close may fail and set errno for any of the errors specified for the library functions chdir(2) and close(2).

The functions Fn fts_read and Fn fts_children may fail and set errno for any of the errors specified for the library functions chdir(2), malloc(3), opendir(3), readdir(3) and stat(2).

In addition, Fn fts_children , Fn fts_open and Fn fts_set may fail and set errno as follows:

Bq Er EINVAL

The options were invalid.